1. Field of the Invention
The present invention relates to improved methods of sealing subterranean zones to remedy the uncontrolled flow of fluids into and from the zones.
2. Description of the Prior Art
In the drilling of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures and other drilling fluid thief zones are often encountered whereby the drilling fluid circulation is lost and drilling operations must be terminated while remedial steps are taken. Also, when a subterranean zone is penetrated containing fluids under a pressure which exceeds the hydrostatic pressure exerted on the zone by the drilling fluid, formation fluid crossflows and/or underground blow-outs can and often do occur.
Heretofore, a variety of methods of sealing compositions have been developed and used for combatting lost circulation, crossflow and underground blow-out problems. However, such methods and compositions have often been unsuccessful due to delayed and inadequate viscosity development by the sealing compositions used. Also, the methods of placement of the sealing compositions have been inadequate to cause plugging of all the weak permeable portions of the zones being treated and to prevent bypassing of such portions by the sealing compositions and/or the wash out of the compositions.
Thus, there is a need for improved methods of placing sealing compositions in subterranean zones to remedy lost circulation, crossflow and underground blow-out problems.